Codonella cratera is one of the most common ciliates in the plankton, which I find in many of my sampling sites. In fresh samples, the specimens are very easy to recognize by their short, jug-shaped or amphora-shaped lorica. To avoid sinking due to the weight of the lorica, the specimens must swim continuously. The lorica is made of an organic, often brownish cement, in which small diatoms and mineral grains are embedded. Diatoms of the genus Cyclotella seem to be preferred. The neck of the lorica is often somewhat constricted or has ring-shaped constrictions.

The ciliate sits on a short stalk at the bottom of the lorica. It is contractile, and the specimens can retract into the lorica when threatened. Food is drawn in with the large adoral membranelles, which also provide propulsion during swimming. The diet mainly consists of small algae, diatoms, and flagellates.